Salmonella typhimurium strains TA97, TA98, TA100, TA1535, TA1537 and TA1538 are being used to test chemicals of interest for mutagenicity. Dimethyl- aminoazobenzene (Butter yellow, DAB) and three of its structural analogues, N-methyl-5-phenylazo-indoline (IND), 4-N-pyrrolidinylazobenzene (PYR), and 4'-diethyl-4-N-pyrrolidinylazobenzene (EPYR); 2,3,7,8-Tetrachlorodibenzofuran (TCDF); two alkylnitrites; 4-chloromethylbiphenyl (4CMB); a lactone and its ester precursors; and 9-aminoacridine (9AA) and quinacrine were tested or will be tested for their mutagenic activity using various in vitro activation systems.